State whether the following statement is True or False:
All objects attract each other along the line joining their centre of mass.

Why does a body weigh more at the poles than at the equator?

Give reason:
$(a)$ Value of '$g$' is not constant on Earth.
$(b)$ Objects with different masses take the same time to fall from a fixed height.
$(c)$ '$G$' is known as the universal gravitational constant.

Suppose a planet exists whose mass and radius both are half that of Earth. Calculate the acceleration due to gravity on the surface of this planet.

$A$ ball is dropped from a height of $20\, m$. $A$ second ball is thrown downwards from the same height after one second with initial velocity $u$. If both the balls reach the ground at the same time, calculate the initial velocity of the second ball. (Take $g = 10\, m s^{-2}$).

$A$ ball is thrown vertically upward,acceleration due to gravity is: